a) Field of the Invention
The present invention relates to a mirror-housing positioning device for a car rearview mirror, and more particularly to an improved mirror-housing positioning device for use in a car rearview mirror having a foldable housing in which a mirror unit is assembled to turn or fold the mirror housing by a motor.
b) Prior-art Statement
Rearview mirrors of which the mirror housing having a mirror assembled therein can be turned or folded to predetermined positions are known from the disclosures in the U.S. Pat. No. 4,919,526 and Japanese Unexamined Utility Model Publication (Kokai) No. Hei-6-49203, for example. In these well-known rearview mirrors, the mirror housing is installed on either side of a car body, and adapted to take three positions: Viewing position (or normal position), and front and rear parking positions (or folded positions). Namely, the mirror housing can be turned with respect to a base fixed to the car body, by hand or as driven by a motor, and swung to the viewing position where it protrudes laterally from the car body and gives the car driver a rear view or to the rear parking position where the outer end thereof is directed toward the tail of the car body while the front side thereof faces generally directly the lateral side of the car body. Furthermore, when the mirror housing set in the viewing position is accidentally pressed by a human body or any other thing, the mirror housing can be turned in relation to the base and swung to the rear parking position or to the front parking position where the outer end thereof is directed toward the head of the car body while the rear side thereof faces generally directly the lateral side of the car body, depending upon the direction in which the mirror housing has been applied with the external force.
Major components of such a mirror-housing positioning device for a car rearview mirror are a stationary member that is to be connected to a base which in turn is to be fixed to the car body, and a rotary member that is connected to the mirror housing. The rotary member is fitted on a support shaft erected on the stationary member. A gear is provided as fitted on the rotary-member support shaft and connected to the stationary member by means of a clutch. A gear train is built in the rotary member to provide a connection between a motor for driving the rotary member and the gear on the support shaft. The gear on the support shaft works as a solar gear while a one of the gears in the train that is in mesh with the gear on the support shaft serves as a planetary gear. As the rotary member is rotated about the support shaft along with the motor and gear train, the mirror housing is tuned to the viewing or rear parking position. When the rotary member has been rotated to a predetermined position where it is blocked from further rotation, a larger current starts flowing through the motor, whereby the motor torque is increased and the gears are engaged at the teeth thereof to each other with no backlash between them. The above-mentioned clutch consists of the gear on the support shaft, a clutch disk disposed between the gear and rotary member, and a clutch spring that forces the rotary member to the clutch disk. When the mirror housing is turned by hand or when it is accidentally pressed by a human body or any other thing while the motor is out of operation, the gear on the support shaft is caused to slide in relation to the clutch disk, and the rotary member can be rotated on the support shaft along with the motor, gear train and the gear on the support shaft.
The gear on the support shaft and those in the gear train employed in these conventional mirror-housing positioning devices are spur gears. The spur gears can be manufactured with reduced costs, and show a higher transmission coefficiency than worm gears do. Therefore, any smaller-power motor commercially available at a lower price can be used in the mirror-housing positioning device. However, when an external force such as vibration of the car body is applied to the mirror housing, one of the gears in the gear train that is in mesh with the gear on the support shaft rotates and revolves, and the motor and gear train rotate reversely, resulting in an easy displacement of the mirror housing from its set position. Also when the mirror housing is turned by hand or when it is accidentally pressed by a human body or any other thing, a part of the force having acted on the rotary member through the mirror housing is consumed for reverse rotation of the gear train and motor. Namely, this loss of force causes the clutch disconnection to not be smoothly done.
Also, the Japanese Unexamined Utility Model Publication (Kokai) No. Hei-6-49203 discloses a mirror-housing positioning device of a similar structure to that of the above-mentioned prior-art positioning devices. In this mirror-housing positioning device, the stationary member has formed therein sector recesses each stepped at both ends thereof. A ball is provided as received in each of these sector recesses. One of these balls is always beneath one of the gears in the gear train provided in the rotary member. A rod, for example, is provided between the gear and ball in such a manner as to be held slidably axially of the gear train in relation to the rotary member. When the mirror housing is turned to the viewing or rear parking position and thus the ball under the gear rides on the step at the end of the sector recess, the rod will slide to raise the gear and thus the other gears on the same gear shaft. Therefore, the gears are forced to each other and to the rotary member. The gears are blocked against rotation.
In this mirror-housing positioning device, when the mirror housing is turned to the viewing position or rear parking position, the gear in the gear train that is nearest to the rod is raised by the rod, and the other gears are also raised one after another and forced to each other. Thus, the gears are locked against rotation. Any vibration of the car body or the like will not cause the mirror housing to displace from its set position. Also, when the mirror housing is turned by hand or when it is pressed accidentally by a human body or any other thing, the clutch disconnection can be done smoothly. In these conventional mirror-housing positioning devices, however, when the mirror housing is turned to the viewing position or parking position, the teeth of each gear are in mesh with each other with the backlash deviated to any one side thereof so that the teeth are strongly forced to each other. Since the force applied to the teeth varies from one gear to another, some of the gears are not moved successfully so that the gear rotation is blocked at one time or not blocked at other time. For a smooth movement of the gears, each of the gears must be machined with a higher precision and the clearance between the gear and gear shaft be accurately adjusted for each gear. These precision machining and accurate clearance adjustment have to be done for all the mirror-housing positioning devices.